Improved bounds for the lazy cops and robbers on generalized hypercubes

Abstract

In Lazy Cops and Robbers, at most one cop moves on each cop turn. We study the lazy cop number of the generalized hypercube $Q(n,m)$, whose vertex set is ${\{0,1,\dots ,m\}}^n$. For each fixed integer $m\ge 2$, we prove the asymptotic upper bound $$c_{\mathrm{L}}(Q(n,m))=O\left(\frac{{(m+1)}^n}{n^{3/2}}\right).$$ This result improves the upper bound of Sim, Tan, and Wong by a factor of $\log n$. The proof combines a moving dominating-set argument with an explicit dominating-set construction inside the support classes of each level. As a separate domination result, we show that, for fixed integers $m\ge 2$ and $d\ge 1$, the Hamming graph $K_m^{\square k}$ has a distance-$d$ dominating set of asymptotic size $O(m^k/k^d)$. This order is optimal up to a constant factor.

5 pages